Electrical contact mapping of the heart typically involves voltage and activation mapping and is accomplished using a standard multi-polar electrode catheter, e.g., a Biosense Webster deflectable tip mapping/ablation catheter (2 mm or 4 mm tip). The catheter is coupled to a processing unit or analyzer, which in turn is coupled to a video display unit. In use, the catheter is inserted, via the Seldinger technique, in the femoral veins and is positioned under fluoroscopic guidance at predetermined locations in the right atrium, right ventricle, coronary sinus and, if necessary, in the left atrium and left ventricle. The mapping catheter is then translocated to between 50 and 200 different point locations throughout the cardiac chamber of interest during the spontaneously occurring or induced arrhythmia which is either a supraventricular tachycardia (SVT), a ventricular tachycardia (VT) or frequent ventricular premature complexes (VPC's). At each point, with the catheter tip in good contact with the endocardial wall of the chamber of interest, the following electrical parameters are measured and registered by the software in the processing unit to their position in 3-dimensional space on the endocardial surface of the chamber of interest: (1) local electrical activation time (LAT) and (2) tissue voltage (V). That system is also capable of measuring tissue impedance (Z). The measurement of tissue impedance, being for the purpose of differentiating scar tissue from normal tissue or fat from scar tissue, and these measurements are made during normal sinus rhythm.
An electro-anatomic activation map (such as shown in FIG. 2) is generated for the LAT and tissue voltage and those parameters are displayed on the video display as an iso-activation and an iso-voltage map. The iso-activation map is evaluated for the pattern of activation as either being centripetal or reentrant. A centripetal pattern is one having a focal area of earliest activation with waves of progressively later activation spreading out concentrically from the earliest activation site. This is compatible with a focus of electrical activity firing off rapidly and activating the rest of the chamber sequentially. The other pattern of activation, i.e., reentrant, shows a well defined region where the tissue with the earliest activation time is immediately adjacent to tissue with the latest activation time, indicating that the chamber is being activated sequentially, and continuously as a large reentrant circuit. The iso-activation map demonstrates activation emanating from one region and then sequentially spreading throughout the chamber and finally the returning to the region of earliest activation, as if inscribing a large circle of the spreading electrical wave front.
Heretofore iso-activation maps have typically been color coded so that red indicates early activation sites, blue and purple indicates late activated sites, and orange, yellow and green indicates intermediate activation sites.
Relying on these different patterns of the iso-activation map to differentiate these arrhythmia mechanisms so that appropriate therapy, e.g., ablation, can be applied to the patient can sometimes be misleading and can cause a lot of wasted time and energy in the effort to define the mechanism of the arrhythmia and direct the ablative therapy. The major problem is that a focal arrhythmia can mimic a reentrant arrhythmia, particularly when the focal firing tissue is in another chamber and the electrical wave fronts that travel into the chamber being mapped cause activation in the chamber of interest in a macroreentrant pattern due to anatomic/physiologic barriers that generate one-way conduction in that chamber. Thus, the iso-activation map in the chamber of interest shows the macroreentrant pattern of earliest activated tissue adjacent to latest activated tissue, while the actual arrhythmia generator is a group of cells focally firing elsewhere. Ablating across the presumed reentrant circuit in this scenario to produce a “line of block” to interrupt the reentrant circuit isthmus and terminate the arrhythmia, will have no effect.
There is reason to believe that the above scenario, particularly if it involves the right atrium, is not so infrequent, as in this chamber there are natural anatomic barriers that can confine the conduction of electric current to a fixed pathway, that would mimic a reentrant activation pattern, with a little help from some physiologic barriers that develop when there is associated organic heart disease that cause fibrosis which can lead to anisotropic conduction and physiologic block.
Thus, there presently exists a need for additional methods and systems for identifying/differentiating arrhythmia sources, e.g., discriminating between focal arrhythmias and reentrant arrhythmias. Additionally, there is utility in identifying coherent, rapidly conducting pathways that may be participating in reentrant circuits and to identify damaged cardiac tissues, i.e., scar tissue, that is often the substrate for micro-reentrant circuits. The subject invention addresses those needs.